Chapter 18.6

Chapter 18.6 - p-type extrinsic semiconductors (I) Excess...

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26 MSE 2090: Introduction to Materials Science Chapter 18, Electrical Conductivity p-type extrinsic semiconductors (I) Excess holes are produced by substitutional impurities that have fewer valence electrons per atom than the matrix. A bond with the neighbors is incomplete and can be viewed as a hole weakly bound to the impurity atom. Elements in columns III of the periodic table (B, Al, Ga) are donors for semiconductors in the IV column, Si and Ge. Impurities of this type are called acceptors, N A = N Boron ~p
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27 MSE 2090: Introduction to Materials Science Chapter 18, Electrical Conductivity p-type extrinsic semiconductors (II) The energy state that corresponds to the hole ( acceptor state ) is close to the top of the valence band. An electron may easily hop from the valence band to complete the bond leaving a hole behind. Conduction occurs mainly by the holes (thus p-type). σ ~ p|e| μ p ~ N A |e| μ p (for extrinsic p-type semiconductors)
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28 MSE 2090: Introduction to Materials Science
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Chapter 18.6 - p-type extrinsic semiconductors (I) Excess...

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